1. Field of Invention
This invention relates generally to multimedia content, and more specifically to multi-bit-rate encoding and transcoding the multimedia content for removable storage devices.
2. Art Background
Portable audio and video players can receive digital media content from a variety of sources. Typically, media content is transferred to the portable device as a download from the Internet or a transfer from a host computer such as a laptop or desktop computer. These portable audio and video players have limited or fixed storage capacity on which the digital media content is stored. The characteristics of the digital media content such as the audio dynamic range, frequency bandwidth, and playtime determine a minimum storage requirement per media item. A media item indicates some quantity of the media and can be a song or an album for example. Similarly, an image quality and a playtime of a video segment will determine a corresponding file size for the video segment.
A raw media stream containing audio and video is formatted for a high quality user experience with devices capable of presenting the high quality user experience to the user. Examples of such devices are wide screen or high definition television, high resolution computer monitors, and compact disk players feeding surround sound audio systems with high dynamic range, wide frequency spectrum audio signals. Media content structured to provide the high quality user experience on the most visually detailed and acoustically sensitive environments places a large demand on the limited storage available on the portable devices such as portable audio and video players. These portable devices typically have removable storage. A non-exclusive list of removable storage includes compact flash cards™, smart media cards™, and micro disk drives.
The portable video player, by its very nature, has a viewing screen that is much smaller than the screen used on a full size television that the media content was originally produced for. Thus, an acceptable user viewing experience on a portable video player can be achieved with a media content encoded at a much lower bit rate than would be required on the full size video viewing devices described above. In like manner, it is often the case that portable audio players are operated in noisy environments that prevent the user from enjoying the full quality of the recorded music because of environmental conditions that present a noise floor that is not present in an optimum listening environment.
Multi-bit-rate encoding has been used to vary the data transfer rate of media content during transfer of the media content over the Internet. Adaptive Streaming Format (AFS™) from Microsoft Corporation and SureStream™ from RealNetworks provide bit-rate scalability ranging from 20 kilobits/sec (Kbps) to over 1 megabit/sec (Mbs) to accommodate the different data transfer rates of the communication links that make up the Internet. MPEG standards can be used to perform encoding at various bit rates as well.
However, the current delivery of media content to portable devices does not include an effective consideration of the parameters of the portable device such as storage size and viewing/listening limitations. The current media transfer schemes to a portable device typically encodes content at the lowest bitrate to accommodate more content or at the highest quality to render the best experience. The user experience is not optimized based on the storage space available and the rendering capabilities of the device.